Air filter units in the form of cassettes or cartridges are well known in the art and find wide use in commercial plants and other areas where harmful particulate matter, dust and the like must be removed from the air. Generally, the air filter units are disposed over a hopper or similar structure for collecting air impurities that fall by gravity. The air itself is drawn into the lower end of the filter cartridge or cassette and passes out the upper end. In this respect, there is normally provided an air duct above the filter incorporating an appropriate blower for moving the air through the filter and back into the room, outdoors or other area.
To clean filters, the normal practice has involved periodically mechanically shaking the filters so that shaken loose impurities will simply fall into the collection hopper. In addition, or as a replacement to the mechanical shaking technique, vacuum cleaning systems of many different types have been proposed. However, such systems as exist have not really been effective particularly where the filter unit has a substantial depth between the entrance and exit air openings and the folds of filter material are too close to permit direct traverse by a nozzle.
More particularly, in vacuum cleaning systems, a vacuum head is simply moved across the entrance air opening of the filter with the hope that impurities will be removed from the filtering material. While some impurities of course are necessarily removed close to the entrance end of the filter, the impurities in the interior of the filter and close to the exit end cannot easily be so removed. As a consequence, for effective cleaning by vacuum, it has been necessary to either diassemble the filter in order to provide access to the interior thereof or, alternatively, design vacuum heads such that they can be physically inserted within the filter to clean surfaces of the filtering material. Neither of these solutions are particularly satisfactory since down time is required during the cleaning operation.
There is a need, accordingly, for a filter cleaning system wherein a vacuum head can readily be passed along the air entrance opening for the filter unit or units to provide effective cleaning without having to disassemble the filter units or design a head for movement within the filter unit. Such a system would have certain advantages not possible with presently available systems. For example, no down time whatever would be required since the vacuum head could be operated while the filter units are still in operation. Moreover, the system would lend itself to automatic timer control for consistent periodic cleaning.